It is the unit for calculating the length of a publication. Half the width of the whole paper (that is, a pair of folio) is printed on both sides, which is called printing paper. A piece of paper in books and periodicals is called a "page", and both sides of a page have two page numbers, so a page has two "faces". On the premise of determining the format, the number of pages of a printed paper is the same, and the number of pages is half. Take a 32-format book as an example: a piece of printing paper has 32 page numbers, ***32 pages, that is, 16 pages. The calculation formula of sheet number: sheet number = page number/page number. If there are decimals when calculating the number of sheets, it is generally necessary to carry them up according to the principle of "making zero pages with less than one sheet in an even state (accounting for four pages)" to facilitate printing and binding.